Traffic noise (road noise, railway noise, aircraft noise, noise of parking cars), is the most dominant source of annoyance in the living environment of many European countries. This is followed by neighbourhood noise (neighbouring apartments, staircase and noise within the apartment). The subjective experience of noise stress can, through central nervous processes, lead to an inadequate neuro-endocrine reaction and finally lead to regulatory diseases. Within the context of the LARES-survey (Large Analysis and Review of European housing and health Status), noise annoyance in the housing environment was collected and evaluated in connection with medically diagnosed illnesses. Adults who indicated chronically severe annoyance by neighbourhood noise were found to have an increased health risk for the cardiovascular system and the movement apparatus, as well as an increased risk of depression and migraine. Furthermore adults with chronically strong annoyance by traffic noise additionally showed an increased risk for respiratory health problems. With regards to older people both neighbourhood and traffic noise indicated in general a lower risk of noise annoyance induced illness than in adults. It can be assumed that the effect of noise-induced annoyance in older people is concealed by physical consequences of age (with a strong increase of illnesses). With children the effects of noise-induced annoyance from traffic, as well as neighbourhood noise, are evident in the respiratory system. The increased risk of illness in the respiratory system in children does not seem to be caused primarily by air pollutants, but rather, as the results for neighbourhood noise demonstrate, by emotional stress.

We have developed towards a "loud" society. Today not only traffic noise, but also leisure and neighbourhood noise affect people, since noise surrounds them nearly 24 hours a day. This can be observed in representative surveys in which the polled persons indicated to what extent they feel disturbed or annoyed about various noise sources [Figure - 1].

The predominant source of noise annoyance in residential quarters is traffic followed by neighbourhood noise. Usually, neighbourhood noises are sounds with high information content such as language, music or also the noise of footsteps. It is in the nature of humans to have their attention drawn to such informative sounds, even if the sound level is relatively low. The annoyance potential of neighbourhood noise is therefore relatively high also at low noise levels and is heightened by the hearer's knowledge of the sound producer and other things causing the noise.

Policymakers, the public and many experts still underestimate the health impacts of noise in the residential environment. Noise can affect the neurological system directly or indirectly through subjective experience (disturbance, annoyance). The consequences are vegetative reactions such as the reduction of the skin's resistance or changes in heartbeat frequency,[2],[3],[4] as well as changed concentrations of the activation hormones adrenalin, noradrenalin and cortisol in body fluids.[5] In this way, metabolic procedures, the regulation of vital body functions and the immune system can be influenced.[6],[7],[8],[9],[10]

The health effects of noise in residential quarters are still underestimated

Noise is not only a physical stimulus, but also an individually experienced noise-event with a corresponding emotional reaction.[11],[12] An insufficient ability to cope with the noise can therefore lead to an inadequate neuro-endocrine reaction[13] and to regulatory diseases. The health effects of permanent noise stress can reveal themselves ten to fifteen years later in different functional systems.[14]

Until now the role noise-caused annoyance plays in the development of health impairments in daily life could not be clarified. Due to conclusion by analogy, it is to be feared that chronic strong noise annoyance could trigger a vicious circle with the elements: annoyance ⇒ negative emotional reaction ⇒ neuro-vegetative-hormonal regulatory disturbances ⇒ illness.

The circle is closed when the illness itself increases the noise annoyance again.

Yet normally the annoyance represents an independent noise effect category, which is characterized by a loss of quality of life.[15] The extent of the health impacts from noise annoyance in the residential environment over a number of years can only be verified using appropriate epidemiological studies. In the LARES survey, noise annoyance was included as a residential environmental factor and its relation to medically diagnosed illnesses was evaluated. The results for traffic noise and neighbourhood noise are presented and discussed in this article.

The LARES Study

The LARES study (Large Analysis and Review of European housing and health Status),[16] was coordinated by the World Health Organization (WHO) European Centre for Environment and Health in Bonn (WHO Regional Office for Europe) in eight European cities from 2002 to 2003, by recommendation of the WHO European Housing and Health Task force in order to fulfil the following objectives in particular:

Improvement of the knowledge about "evident" or assumed effects of housing conditions on health and on physical, social and mental well-being (noise-induced annoyance was considered as part of such residential impacts);

Evaluation of the quality of European housing stock in a holistic way, as well as the setting of priorities in the evaluated cities and the identifications of general trends;

Development of a "practicable" instrument to evaluate the effects of housing conditions on health in cities or regions in Europe.

The LARES study consisted of three instruments overall: the inhabitant questionnaire, the inspection sheet and the health questionnaire.[16]

The inhabitant questionnaire was filled in during an interview with one resident of the examined household. The inhabitant questionnaire was used to collect data regarding the perception of the dwelling and the perception of the immediate residential environment.

The inspection sheet was carried out by trained interviewers in order to obtain technical and objective data about the examined dwelling.

The health questionnaire was finally filled in by every member of the examined household to include the health information of all residents.

The choice of the households was carried out randomly in each of the eight European cities. The execution of the study as well as the data collection was supervised by WHO in each city in the same way [Table - 1].

The objective of the LARES study was to register the data of roughly 400 households with about 1000 inhabitants in every city. Overall, 1079 variables in 3382 households were collected from 8539 people [Figure - 2].

Annoyance and chronic diseases in the LARES study

The individual annoyance by outdoor and indoor noise sources was determined by the question, "Thinking about the last 12 months, when you are at home, how much would you say noise from the following sources bothers or annoys you?" The strength of noise annoyance was rated by the five-step International Commission on Biological Effects of Noise (ICBEN) scale of "none" to "extremely" (compare with [Figure - 1]. The percentage distribution of the annoyance for neighbourhood and traffic-related noise sources is represented in [Figure - 3], divided into the five annoyance categories.

[Figure - 3] shows that about 39% of the surveyed persons were annoyed by the traffic noise (9% indicated "strong" or "extremely strong" traffic noise), closely followed by neighbourhood noise with approximately 36%. Aircraft noise ranks fourth with 13% of the surveyed persons; railway noise reached the fifth place with 6.8%. Note that the survey included airport and railway areas, but did not concentrate on areas specifically troubled by aircraft or railway noise. What is surprising is the high portion of residents (21%) who felt annoyed by noise, vehicles made when parking. This noise source achieves position three, with values of 21% of the surveyed people.

The individual annoyance by road noise, aircraft noise and railway noise as well as the annoyance by parking vehicles were summarized under the term "general traffic noise" because traffic noise represents the dominant source of noise in residential areas and the majority of respondents indicated that they were troubled by more than one source of traffic noise. Each of the mentioned traffic noise sources was collected with the five-step ICBEN scale (1 to 5 points). Therefore the overall-variable traffic noise annoyance ranges from 4 to 20 points. This overall variable was divided into three categories (none at all, moderate, and severe annoyed). People with more than eight points were classified as severely annoyed. The second greatest source of noise in residential areas is neighbourhood noise. Noise annoyance from neighbours, stairways, playing children as well as noise occurring within the dwelling were summarized under the term "general neighbourhood noise". The overall variable neighbourhood noise annoyance was divided into three annoyance categories in the same way as in the case of traffic noise annoyance. Both three-step variables were used in the statistical analyses (In previous presentations we used the term strongly annoyed. To avoid further confusions regarding the ICBEN-scale we change to the term severe annoyance). The questions "Have you had one of the following diseases in the last 12 months?", and "Was the illness diagnosed by a physician?" were used in the LARES study to access the period prevalence of 16 medically diagnosed illnesses. The prevalence of selected illnesses in adults and in the elderly is represented in [Figure - 4].

The results show that hypertension and allergies were the most frequently medically diagnosed illnesses for adults (12.1% and 11%, respectively), followed by arthritis and migraine (9.6% and 9.5%, respectively). Depression was reported by 6.1% of the respondents.

In the elderly participants in the LARES study, hypertension and arthritis were the most frequently indicated medically diagnosed illnesses, with a prevalence of 41.7% and 37.5%, respectively. This was much higher than for the adults group. Bronchitis (11.4 %), migraines (11.3 %) and depression (10.1 %) followed with decreasing frequency. The prevalence of illnesses was again markedly higher in the elderly.

Substantial differences were also observed within the results for children. The LARES Study revealed that in children mostly allergies were diagnosed (11.7%), followed by asthma (4.4%), bronchitis (3.6%) and migraine (3.6%). With the exception of allergies, bronchitis und skin diseases, the prevalence of illness in children were markedly less than in adults [Figure - 5].

Materials and Methods

The period-prevalence (medical treatment in the last 12 months) was evaluated with regards to the severity of the noise-induced annoyance. In all analyses, multiple logistic regressions were used. "Odds ratios" (OR) were calculated for estimating the relative risk (An Odds ratio can be interpreted as a factor, for which the chance to fall ill increases for exposed persons. The interpretation is analogous to that of the relative risk; only the concept of the risk is replaced by the concept chance). For categorical variables, the category with the lowest burden was chosen as reference. Due to the different disease prevalence in children, adults and the elderly (compare with [Figure - 4],[Figure - 5], the age groups were evaluated separately.

The evaluation integrated block-wise 13 control variables with expected influences on the result, such as age, sex (basic block), socioeconomic state (block 2) and alcohol consumption, body mass index, tobacco usage, physical activity (block 3). These classic control variables were completed with housing condition factors. A comprehensive statistical check of the noise effects with regards living and residential environment factors such as "humidity in the habitation" (mold), "housing temperature in the winter," "air quality in the habitation," "daylight in the dwelling" (block 5) as well as "green areas in the residential environment" and "satisfaction with the residential environment" (block 4) became possible for the first time in the LARES Study.

Differences between European cities were taken into account by using the variable "city" in the basic block. Neighbourhood noise annoyance was used within the basic model as a control variable if traffic noise-induced annoyance was evaluated. Traffic noise induced annoyance was used as a control variable if neighbourhood noise-induced annoyance was evaluated. Considering the multitude of the examined illnesses, the extensive control variable set is not to be considered complete. Although this has to be taken into consideration when interpreting the statistics of the individual noise effects, the LARES study is probably the first to enable the integration of such a wide range of confounders.

Results for Annoyance Caused by Traffic Noise

In the following figures the relative risk of illness (OR), including a 95% confidence interval, is represented for people who have felt annoyed by traffic noise in the last 12 months. This is compared with people in the same age group who did not indicate any annoyance from the analysed noise source (comparison group). A recorded relative risk (OR) is statistically significant if the associated confidence interval does not include the value 1. Furthermore, the values of the OR are specified in the diagrams beneath the confidence intervals. The numbers of observed diseases (N) are recorded above the confidence intervals and the level of significance for a linear trend (1 d.f.) within the annoyance categories is specified in the middle of the diagrams.

Adults

The LARES study confirms that chronic annoyance from traffic noise can be associated with an increased risk to the cardio-vascular system in adults (18 to 59 years). A significantly higher risk of "cardiovascular symptoms" (CV-symptoms) as well as of "high blood pressure" (hypertension) was shown in subjects severely and chronically annoyed by traffic noise [Figure - 6].

The trend within the annoyance categories (from "not at all" to "severely") was significant and supports a dose-effect relationship between hypertension and chronic annoyance induced by traffic noise. No increased risk was found for medically diagnosed heart attacks.

The effect of severe and chronic annoyance by traffic noise was not only seen in the cardiovascular system, but also, for example, in the respiratory system [Figure - 7]. Significantly increased risks were recorded for "respiratory symptoms" as well as for "bronchitis" in conjunction with severe and chronic annoyance by traffic noise. A significant, positive trend within the annoyance categories (from "not at all" to "severely) also appeared. In contrast, no significant trend within the annoyance categories could be seen for asthmatic diseases.

The effects of a chronic annoyance by traffic noise were also revealed in the stress-sensitive locomotor system [Figure - 8]. Significantly increased risks were registered for "arthritic symptoms" as well as for "arthritis" when severe and chronic annoyance by traffic noise is reported. The trend within the annoyance categories (from "not at all" to "severely") was significant in each case. A significantly increased risk towards allergies was also shown with severe and chronic annoyance by traffic noise. Here too the trend over the annoyance categories reached a statistical significance [Figure - 8].

The effects of severe and chronic annoyance by traffic noise were very pronounced in the neuro-psychic system [Figure - 9]. The trend towards depression (based on sleep disturbance, anhedonia, low self-esteem and appetite change measured with the SALSA screening tool) [17] as well as medically diagnosed depressions appeared frequently in conjunction with severe and chronic noise annoyance. The trend within the annoyance categories was highly significant. Furthermore, an increased risk of migraine was seen with severe and chronic noise annoyance. Here too the trend within the annoyance categories was highly significant.

The elevated health risks due to severe annoyance by traffic noise reveal that a very noisy residential environment must be classified as a serious health risk for adults.

The elderly

Stress research shows that the ability to cope with stress decreases with age. In this context, elderly people are often considered a potential risk group. The results of the LARES Study cannot confirm an increased illness risk for the elderly (people aged 60 years and older). No statistical association could be shown between chronic annoyance by traffic noise and an increased risk for the cardiovascular system of elderly adults [Figure - 10]. This applies also to respiratory and neuro-psychic systems.

In elderly people, the effect of chronic annoyance by traffic noise was only apparent in the locomotor system [Figure - 11]. For elderly people who indicate severe and chronic annoyance by traffic noise a significant increased risk for arthritic symptoms and arthritis were recorded. The trend within the annoyance categories was highly significant.

The results of the LARES-study do not verify that older people represent a risk group with regard to health impairment by traffic noise-induced annoyance.

Children

Many functional systems in small children (e.g., the nervous and the cognitive systems) are subject to rapid growth and intensive development phases during which neural structures develop and abilities are acquired. The development of the child is not designed to compensate for high environmental noise exposure. In such cases there stands a high risk for lasting dysfunctions. Beyond that, with early exposure to environmental influences, children have significantly more time to develop chronic illness. As a result, children can be regarded as an independent risk group.

The results of the LARES study reveal a close relationship between severe and chronic annoyance by traffic noise and disorders of the respiratory system in children. When severe and chronic annoyance by traffic noise is reported, significantly high risks were noted for respiratory symptoms as well as for bronchitis [Figure - 12]. The trend within the annoyance categories was significant. The trend within the annoyance categories was significant.

The risks were higher for children who indicate severe annoyance by traffic noise (2.1 to 2.3) than the corresponding risks for adults (compare with [Figure - 7]). A higher risk for asthma for children was not identified.

The highly increased risks for illness in the respiratory system support the assumption that children are a risk group regarding traffic noise-induced annoyance.

Results for Neighbourhood Noise

At present there are no available epidemiological studies on the health effects of chronic annoyance by neighbourhood noise. Due to the pathogenesis mechanisms presumed today, it was to be expected that the health effects of a chronic annoyance are dependent on the severity of the annoyance, but only insignificantly dependent on the noise source of the annoyance. The evaluation of the LARES-study regarding the annoyance by neighbourhood noise made examining this thesis possible.

In adults, chronic annoyance by neighbourhood noise was related to increased risks for the cardiovascular system, as was the case for traffic noise [Figure - 13]. Significantly increased risks appeared for cardiovascular symptoms and hypertension in conjunction with severe and chronic annoyance by neighbourhood noise. The trend within the annoyance categories was likewise significant. However, an increased risk of heart attack could not be confirmed.

For the respiratory system, the effect of severe and chronic annoyance by neighbourhood noise was less clear than that of severe and chronic annoyance by traffic noise [Figure - 14]. Only the risk of bronchitis appeared significantly increased. However, a positive trend within the annoyance categories could not be confirmed in instances of annoyance by neighbourhood noise. Furthermore, an increased risk for asthma through neighbourhood noise annoyance could not be confirmed, nor was it evident in the case of traffic noise annoyance.

Pronounced effects of severe and chronic annoyance by neighbourhood. noise were obvious in the stress-sensitive musculoskeletal system [Figure - 15]. Highly increased significant risks were calculated for arthritic symptoms as well as for arthritis. The trend within the annoyance categories was highly significant. In contrast to that, an increased risk for allergies by neighbourhood noise annoyance was not evident.

Distinctive effects on the neuro-psychic system were also registered with chronic annoyance by neighbourhood noise [Figure - 16]. The trend for depression (SALSA) as well as medically diagnosed depressions significantly increases with severe and chronic annoyance by neighbourhood noise. The trend within the annoyance categories was highly significant. Beyond that, a highly increased risk of migraine was confirmed with severe and chronic annoyance by neighbourhood noise. The trend within the annoyance categories was here also highly significant.

The results of the LARES study in relation to severe annoyance by neighbourhood noise demonstrate that neighbourhood noise must be classified as a serious health endangerment for adults.

The elderly

The results of the LARES study regarding neighbourhood noise annoyance cannot confirm an increased illness risk for elderly people. The statistical analyses showed no association between a chronic annoyance by neighbourhood noise and increased risks for the cardiovascular system [Figure - 17]. This also applies to the respiratory and neuro-psychic systems.

As with traffic noise, the effects of a chronic annoyance by neighbourhood noise for the elderly mainly registered in the locomotor system [Figure - 18]. Elderly people who indicated severe and chronic annoyance by neighbourhood noise had a significantly increased risk for arthritic symptoms. The trend within the annoyance categories was here highly significant. A significant trend within the annoyance categories of the annoyance could be confirmed also for arthritis as well as for allergies.

Regarding annoyance by neighbourhood noise, the results of the LARES Study cannot confirm that elderly people should be classified as risk group.

Children

A chronic annoyance by neighbourhood noise showed a strong effect with children (up to 17 years) in the respiratory system [Figure - 19]. Significantly increased risks were confirmed for respiratory symptoms as well as for bronchitis. The trend within the annoyance categories was highly significant in both cases, whereas a significant increased risk for asthma for children was not identified statistically.

For children who reported severe annoyance, the relative risk of respiratory symptoms or bronchitis were 2.3% and 3.6%, respectively, a markedly higher risk than in adults [Figure - 14].

The strongly increased illness risk in the respiratory system supports the assumption that children should be classified as a risk group regarding annoyance by neighbourhood noise.

Discussion

The disease as a pathological health end-point is of high importance and can only be examined in epidemiological studies. However these epidemiological studies like the LARES Survey only identifies statistical associations. The evaluation of whether an observed association reflects a causal relation must be made on the basis of different criteria.

After exclusion of coincidence, systematic errors (bias) and confounding factors, the strength of the association (relative risk), as well as the biological plausibility, would constitute the main support of a causal relationship. Biological plausibility means that convincing findings exist, which explain how noise annoyance can contribute to the development of illness. Furthermore, for safe point estimation it is necessary that the confidence-intervals are not too large. Lastly, the causality of an interrelation can be supported by confirming a dose-effect relationship.

Furthermore, LARES is a cross-sectional study. The main advantage of cross-sectional studies is that they can have a short duration and it is possible to generalize the results if a representative random sample is used (as in the eight European cities). On the other hand, cross-sectional studies are not optimal for researching the cause of diseases since the simultaneous collection of data cannot establish the chronology of exposure and illness. An advanced exposure is needed to clearly identify that the illness is caused by the exposure. Regarding long-lasting and more common diseases (e.g., chronic bronchitis, high blood pressure, arthritis, etc.) as well as "long-term habits" as risk factors (e.g., annoyance in the last 12 months, smoking behaviour, living conditions, etc.), the use of cross-sectional surveys is nevertheless reasonable if the temporal progression is not in doubt, e.g., due to biological plausibility.[18] Cross-sectional studies are less suitable for rare diseases or diseases with short duration. If the LARES survey and its results regarding the health consequences of noise annoyance are viewed with consideration of these criteria, it can be established that not all of the conditions, but many of them, could be used for clarifying the causality. It is highly plausible that coincidence and bias have been eliminated due to the random sampling and quality control of the WHO. The analysis of the data took place with an extensive control variable set, which for the first time paid attention to the influences of housing conditions. However, the control variable set cannot be considered complete in view of the multiplicity of the examined illnesses. Well-known variables are missing such as hereditary predisposition or occupational noise exposure. In view of comparable investigations, the control of disruptive influences can be rated as altogether very comprehensive.

The biological plausibility is at hand due to knowledge from psychophysiology[19] as well as psychosomatic medicine[20] and by results of the research on emotional activation[21] and stress research.[22] The causality is furthermore supported by dose-effect relationships. Thus the relative risks for cardiovascular impairments (hypertension, cardiovascular symptoms) are clearly increased during chronically severe noise annoyance; during a moderate noise annoyance the risks are less or not different to the reference group. For respiratory impairments (bronchitis, respiratory symptoms), a clear increased risk is registered in conjunction with severe noise annoyance, whereas an increased illness risk can arise already with moderate traffic noise annoyance. Also the risk for arthritis, depressions and migraine rises during chronic noise annoyance in the sense of a dose-effect relationship. The multifarious dose-effect relationships strongly support the acceptance of causality.

With the same equivalent continuous sound level, the intensity of annoyance depends on the kind of acoustic source.[23] On the basis of today's implied pathogenesis mechanism, it is however not to be expected that the health consequences from chronic annoyances of similar intensities depend on the kind of annoyance source. This question can be pursued within the LARES study by a comparison of the calculated relative risks for chronic annoyance by traffic and neighbourhood noise, in which equal annoyance intensities are compared [Table - 2]. The illness risks with severe and chronic annoyance do not differ substantial according to the source of their annoyance [Table - 2]. Exceptions are the respiratory system and the movement apparatus. Regarding the respiratory system it is to be noted that air pollutants, which in traffic have the same origin as the noise, could be responsible for the increased risk. The increased risk with traffic noise seems to be attributable to this strong connection. With neighbourhood noise, for which there is no close connection with traffic-caused air pollution, a significantly increased risk for bronchitis was seen in association with strong annoyance [Figure - 14]. However a trend (dose-effect relationship) could not be statistically confirmed. The results pointed to a combination effect from noise and air pollution that has not been sufficiently researched.

Furthermore, slight specific differences cannot be excluded. The effects of severe and chronic annoyance by neighbourhood noise on the musculoskeletal system seem to be stronger than annoyance by traffic noise. In this case, the strong emotional components of neighbourhood noise could be a factor.[24]

If the two adult groups are compared independently of the noise source, increased risks for adults can be identified in the cardiovascular system, the locomotor system, depressions and migraine. In contrast, elderly people showed increased risks mainly in the locomotor system (arthritic symptoms) but not in the cardiovascular system. Comparable age-dependencies can be found in other epidemiologic studies too, such as in the Spandauer-Health Survey should an evaluation be conducted in the corresponding age divisions.[25]

The Spandauer-Health Survey shows a significantly increased risk for hypertension in adults (adults defined as 20-59 years) with an increasing nightly noise level. This relation could not be determined statistically for elderly people in the Spandau-Survey (more than 60 years; [Figure - 20]).

For these results it should be kept in mind that the examined illnesses of elderly people increase greatly due to age, with or without noise annoyance [Figure - 4]. Thus, variable individual influences can in this way prevent an existing relation between severe annoyance and frequency of illness from being statistical identified.

The results for children show a clear association, particularly between bronchitis and severe annoyance by traffic noise.Such association was also confirmed in a study that was conducted in the Harz Mountains region of Germany.[26] In this Harz study, the production of stress hormones in the first and second part of the night and the frequency of respiratory illness were analyzed. The children with strong annoyance lived on a main street where a truck passed every 2 minutes on average with Lmax > 80 dB(A). The comparison group consisted of children in the same towns who lived in areas with less traffic. The existence of bronchitis and bronchial asthma had a significant correlation with traffic in the Harz study. Since the traffic emissions (noise and air pollution) are highly correlated, these components could not be evaluated separately.[27]

The LARES survey documented the association between respiratory illnesses in children and severe annoyance by traffic as well as with neighbourhood noise [Table - 3]. This is illuminating, since neighbourhood noise as opposed to traffic noise is not connected to traffic-caused air pollution. For children, the development of bronchitis does not only seem to be caused by the air pollutants but also by emotional stress, such as can be seen in the case of the neighbourhood noise annoyance.

In principle, the medical evaluation of the results of the LARES Study must assume that a strong chronic noise annoyance produces psychological stress in the sense of negative emotionality, which is expressed in annoyance, fear, hopelessness, helplessness, aversion, rage or despair. The emotional forms of expressions can be converted into reactions that show up in the neural, hormonal and immune systems, as well as in the basic substance of the extracellular matrix (connective tissue).[12],[20],[21],[28] Birbaumer and Schmidt among others report[29],[30],[31] that chronic emotional stress can cause increased production of endogenous opiate (endorphine, enkephaline). This can result in the inhibition of immune system processes, for example, the activity of killer cells. Ader and assistants[32] lay great importance on conditioning procedures in this connection and describe the influence of a changed psycho-neuroimmunological process on the emergence of asthma.[33] According to Miltner et al.,[34] disturbed psycho-neuroimmunology has to be taken into account in relation to depression. They found clear changes in all of the examined immune parameters, especially in cases of helplessness and hopelessness. What must also be considered in association with the emergence of the diseases mentioned above is the basic substance of the extra cellular matrix, which is considered the underlying system for the basic regularization of a highly developed organism[35],[36],[37],[38] and which is also the location of the non-specific immune system.[35],[39],[40],[41],[42],[43],[44]

Permanent or chronically repeating short-term distress can lead to dysfunctions in the basic substance of the extra cellular matrix so that fibroblasts synthesize unphysiological collagen structures. In this way distress can lead to unspecified pre-aging of the entire connective tissue in the form of a sclerosis. Hauss et al. could demonstrate[44] that after laboratory animals exposed to noise, a sclerosis resulted within a short time due to increased collagen synthesis by fibroblasts. The effects of chronic noise exposure on the immune system of mice are additionally reported.[45]

The connections between chronic noise disturbance and different chronic diseases pointed out in the LARES study, in which the connective tissue is effected, such as blood arterial changes (arterial hypertension), arthritis, as well as bronchitis, could be explained by the dysfunction of the basic substance of the extra cellular matrix and the resulting sclerosis.

Conclusion

The results of the LARES study - with regard to criteria for causal relations - confirmed, on an epidemiological level, an increased health risk from chronic noise annoyance. It has to be assumed that chronic noise annoyance is not only connected with a risk for cardiovascular symptoms, but also with risks for respiratory symptoms like bronchitis as well as arthritis and migraine. With this background, it is urgent that noise in residential areas is reduced to an acceptable level.

Particularly the reduction of traffic noise is connected to problems in residential areas. Solutions for traffic noise problems are often sought in technical sound insulation measures (forced ventilation, sound-proofed windows) that reduce traffic noises in living and sleeping rooms to an "inoffensive" degree. These measures decrease the level of traffic noise-induced irritation indoors but inevitably do not solve the general annoyance problem because the outside areas can not be protected technically against noise and life in a "fish bowl" does not corresponded to residents' expectations. Noise-induced irritations in the outside area seem to be just as important as noise irritations in the inside area for the general annoyance rating. In the future, therefore, exact data must be worked out.[46]

Beyond that, the noises inside the house are perceived as stronger because of high sound insulation of the outside noises. This way, the already considerable problem of neighbourhood noise increases is significance in multi-family dwellings. In this context, increased requirements of the sound insulation between dwellings should be accepted as obligatory in multi-family dwellings.[47]

In a nutshell, the increased illness risks from chronically severe noise annoyance by traffic and neighbourhood noise show that health endangerment in traffic-loaded housing areas cannot be solved only with technical facade insulation measures.

Final Conclusion

In order for the LARES study to answer the question about noise-induced annoyance, it was necessary to experience and process the induced disturbances and/or noise-induced irritations consciously. That is not always the case, e.g. for disturbances of sleep. Noise-induced annoyance has therefore a larger proximity to noise exposure by day than for nocturnal noise exposure. The role of the noise-disturbed, not-restful sleep as a nocturnal pathogenesis mechanism, which is not the subject of this article, is analyzed in an independent publication.